Metal surfaces generally are provided with various chemical treatments to provide desirable properties. The metal surfaces which may be treated include sheets, roll stock, coil stock, etc., or formed metal surfaces such as beverage containers (cans), structural materials for buildings, etc.
Metal cans such as aluminum cans are commonly used as containers for a wide variety of products. After the cans are formed, they are typically washed with various cleaners to remove aluminum fines and other contaminants from the surface. One undesirable result of these treatments is that water often is retained on the clean, rinsed metal cans which represents a major heat load for a dry off oven. For example, about 2.5 grams of retained water per metal can at a production rate of 2500 cans/minute represents over 200,000 kcal/hr. (8000 BTU/hr.) of energy input. Reducing the water load reduces the energy required. Additionally, faster drying may also allow an increase in production rate.
Conventional washes frequently result in a surface finish on the outside of the cans which has a deleterious effect on the efficient movement on the cans through the conveyor systems and onto or off the printer mandrels. It is important, therefor, in the can processing industry, and in particular, the aluminum can processing industry to reduce the coefficient of friction on the outside surface of the cans to improve their mobility without adversely affecting the adhesion of printing, paints or lacquers applied thereto. Cans characterized as having poor mobility generally have higher coefficients of static and kinetic friction. In the commercial can processing operation, there are numerous locations where the cans stop moving momentarily and must start again from rest. The mobility problem is particularly important when the cans are loaded on and ejected from the mandrels of high-speed printers. Other locations in the manufacturing process where the mobility problem is evident is where cans flow through the single file conveyors called "single filers." A high coefficient of static friction generally prohibits an increase in line speed, production speed and production output, results in frequent jammings and printer misfeed problems, and a general loss of production due to increased rates of damage to the cans.
A reduction in the coefficient of static friction on the outside surface improves can mobility through the conveyor systems, especially the single filers. A reduction in the coefficient of static friction (C.O.S.F.) also results in reduced printer rejects. It is therefore desirable to reduce the liquid residue remaining on cans after various aqueous treatments and to improve the mobility of the cans through the can processing equipment.
Thus, a need has arisen in the aluminum can manufacturing industry to modify the coefficient of static friction on the outside surface of the cans to improve their mobility without adversely affecting the application of paints or inks. The reason for improving the mobility of aluminum cans is the general trend in this manufacturing industry to increase production without additional capital investments in building new plants. The increased production demand is requiring can manufacturers to increase their line and printer speeds to produce more cans per unit of time.
A number of patents have described procedures and chemical treatments for improving the mobility of formed metal surfaces, particularly beverage containers. These patents generally describe lubricants and surface conditions for formed metal surfaces which are capable of improving the mobility of aluminum cans without adversely affecting the adhesion of paints or lacquers applied thereto.
U.S. Pat. No. 4,599,116 describes an alkaline cleaning process for aluminum container surfaces. The aqueous alkaline cleaning composition contains an alkalinity agent, a complexing agent to chelate at least some of the metal ions removed from the metal surface by the cleaning solution, and at least one surfactant to remove organic soils from the surfaces of the container and to inhibit white-etch staining of the surfaces. The reference indicates that following cleaning a conversion coating can be applied to the surface of the can and the application of this conversion coating enhances the mobility of the cans as they are conveyed through track work.
U.S. Pat. Nos. 4,859,351; 4,944,889; 5,030,323; 5,064,500; and 5,080,814 describe lubricant and surface conditioners for application to aluminum cans. These patents indicate that the disclosed compositions reduce the coefficient of static friction on the outside surface of the cans which enhances mobility and thereby permits an increase in production line speed. The lubricant and surface conditioners disclosed in these patents are water-soluble alkoxylated surfactants, namely, organic phosphate esters; alcohols; fatty acids including mono-, di-, tri-, and poly-acids; fatty acid derivatives such as salts, hydroxy acids, amides, esters, ethers and derivatives thereof; and mixtures thereof. The references state that the lubricant and surface conditioner may be applied to the cans during the wash cycle, during one of the treatment cycles, during one of the rinse cycles, or after the final water rinse. Both acidic and alkaline wash cycles are disclosed.
U.S. Pat. No. 5,061,389 discloses a composition and process for reducing the coefficient of friction on the surface of formed metal structures, such as aluminum cans, by lubricating the surface with a blend of a polyethylene glycol ester with a fluoride compound.
U.S. Pat. No. 5,286,300 (Hating et al) describes a composition useful as a rinse aid for metal surfaces and for improving the mobility of formed metal surfaces. The composition comprises (A) from about 10% to about 90% by weight of at least nonionic polyoxyalkylene glycol comprising poly(oxypropylene)hydrophobic groups and poly(oxyethylene)hydrophilic groups, and (B) from about 10% to about 90% by weight of at least one alkoxy derivative of at least one ethoxylated and propoxylated glycol. A process is also described for improving the drainage of water for metal surfaces and for improving the mobility of formed metal surfaces.
Current EA regulations are requiring reductions in the amount of volatile organic content (VOCS) that paints and lacquers may contain. In the past, the majority of water-based coatings used in two-piece aluminum beer and beverage can industry had a VOC of about 3.6 lb./gal. Or higher. Environmental regulations now require that the VOC content of such water-based coatings be reduced to about 3.1 lb./gal. Or lower. It is well known in the can industry that satisfactory metal coverage becomes increasingly more difficult as VOC is reduced. In order to reduce the VOCS, the amount of solvent such as Butyl Cellosolve that are used in the coating compositions is significantly reduced. These solvents are more tolerant of the metal surfaces that are contaminated with organics such as mill oils applied on the coil or lubricants that are used in the process of forming the cans. The hydrophobic properties of the lubricant contamination does not allow the low VOC lacquers to wet the surface of the metal as evenly as the solvents. One method for overcoming this problem is to subject the metal surfaces to extra cleaning steps to lower the organic contamination level. The present invention enables low VOC lacquers to be more tolerant of these hydrophobic contaminates.